The invention relates to a protective device working in a contact-free manner for the securing of a danger zone of a machine or the like.
Known safety light grids serve, among other things, for the protection of a respective operator or other persons against dangers which arise from machinery or the like, for example as a result of fast movements of mechanical parts such as with presses. A corresponding safety light grid is set forth, for example, in IEC 61496. A protective optical field is produced by a plurality of transmitter and receiver elements. It can be formed, for example, between transmitter and receiver units separated from one another or, for example, between a combined transmitter/receiver unit arranged on a side of the protective field and a reflector unit. A respective intrusion into the protective optical field, or the interruption associated therewith of at least one light ray, as a rule results in a switching off of the so-called secure outputs (OSSDs=output signal switching devices) of the protective device working in a contact-free manner. A machine stop is triggered by a direct linking of these outputs in the stop circuit of the machine in question on a corresponding intrusion into the protective optical field.
So-called “intelligent” light grids (cf. e.g. DE 44 24 537 A1) have additional functions such as “blanking” (blocking out of defined regions) and “reduced triggering” which make it possible for the triggering of an alarm or of a switch-off signal, which would normally take place, to be prevented for certain intrusions into the protective optical field.
Light grids have also already been proposed with additional functions such as a “cycle control” or a “PDSI” (presence sensing device initiation) which can be used with machines which run through individual cycles which are only started after release by means of an electrical signal. One or more intrusions into the protective field can now be utilized during a non-dangerous part of the machine cycle for the generation of a release signal for a new machine cycle due to the cycle control or PDSI function. The intrusions into the protective field in question must take place in any case to insert and/or remove workpieces, for example, into and/or from the machine. The productivity of the machine in question can therefore be increased correspondingly by such a cycle control or PDSI function, since the previously required additional manual release of the machine is dispensed with.
A cycle control or PSDI function was previously always only used for the whole protective optical field of the light grid in question; that is, the whole protective field of the light grid was previously always used for the cycle control. However, interruptions which should be used for the cycle control are, as a rule, only those which are in the region of the hands or arms of the persons to be protected. Other interruptions can result in a false start of a machine cycle and damage the respective workpiece and/or the respective machine parts.
To be able to evaluate the regions in question differently, it would for example be possible to install two light grid systems with different protective fields and to connect them to a control unit and thus only to trigger a cycle when the light grid with the shorter protective field height corresponding to the region of the hands or arms is interrupted. Such a solution, however, now has a number of disadvantages. For instance, a corresponding design is complex and expensive. The regions in question are fixedly defined by the size and/or the protective field height of the light grids and require a great deal of construction space at the machine where, generally, there is relatively little space available.